Natural gas is often transported in the form of liquid natural gas (“LNG”). LNG usually is primarily composed of methane, but also comprises lesser amounts of heavier hydrocarbons, such as ethane, propane, and heavier hydrocarbons. When LNG is off-loaded at a terminal, it is often desirable to separate ethane or other heavier hydrocarbons from the LNG in the form of natural gas liquids (“NGL”). The separated NGL can be treated as Y-grade product, or can be further processed in a deethanizer to produce both an ethane product and a Y-grade product.
However, it is also desirable to reduce the power consumption involved in separating NGL from LNG. This process typically requires a flash absorber and a demethanizer. LNG terminals will typically have low level heat available for reboiling, therefore it is desirable to operate the demethanizer at a lower than normal pressure to efficiently utilize the available energy.
It is desirable to use a cooled portion of the LNG product stream to reflow to the flash absorber. Additionally, to operate the demethanizer at a lowered pressure, it is desirable to use a portion of the LNG product stream to reflow to the demethanizer to aid in the removal of NGL from the LNG. Demethanizer feed preheaters and side reboilers are desirably utilized to reduce the duty cycle of the demethanizer bottom reboiler.
It is an object of the invention to separate NGL from LNG in a cost-effective process.
It is a further object of the invention to separate NGL from LNG using a demethanizer at a relatively low pressure.
It is yet another object of the invention to efficiently recover at least 90% of the ethane from a LNG feed.